Such a redundantly designed automation system for controlling a technical process is used in areas of automation engineering in which heightened requirements are placed on the availability and reliability of the automation system. These are areas in which shutdown of the plant carrying out the technical process would be extremely costly or could be hazardous for the personnel involved or the environment. A redundantly designed automation system of this kind is also termed high-availability. It is employed, for example, in the chemical industry or for operating a power plant. The automation system contains two separately operating control devices with which central functions for controlling the technical process are redundantly designed. Under fault-free conditions, the two control devices usually execute identical programs for controlling the process. These programs contain function blocks by means of which the functions for controlling the technical process are implemented. Such function blocks are e.g. logic functions such as an AND function, arithmetic functions, a counting function, a monitor function with which, for example, a temperature overshoot can be monitored, etc. The function blocks are concatenated or interconnected in the program. The programs and their function blocks are cyclically and synchronously executed, synchronously meaning that internal states of the function blocks occurring when the function blocks are executed are identical in the two control devices. In the case of a counting function with a counter as the function block, the latter's internal state is e.g. a counter reading. Only one of the two control devices is active at any one time, i.e. only the active control device is actually actively controlling the technical process via its output control data. The other control device is in a passive state. In order to keep the passive control device constantly updated with the reading of the active control device, input data is also fed to the passive control device prior to the start of each cycle. This input data usually comes from field units or other in some cases redundant control devices. Such field units, or field devices, are usually external units or devices such as sensors or actuators. In the event of a malfunction in which a fault occurs in one of the control devices, or when one of the control devices is undergoing maintenance, operation is switched from the affected control device to the unaffected control device so that the latter continues to control the technical process.
When the fault has been cleared or maintenance is complete, the shut down control device must be restored to the current reading of the control device currently controlling the technical process. For this purpose, all the internal states of the function blocks of the control device currently controlling the process must also be assigned to the function blocks of the shut down control device. To do this, control of the process is usually interrupted at the start of a particular cycle. During said interruption, all the information about the internal states is transmitted all at once to the shut down control device by the control device that has been controlling the process prior to the interruption. As it takes a certain period of time to transmit the information about the internal states, the program with which the technical process is controlled by the control devices disadvantageously cannot be executed during this period of time. In order to minimize this time, the information about the internal states of all the function blocks is first packed, i.e. aligned together, written to a special memory area and then the packed data is copied to the shut down control device. The start addresses of the information about the internal states assigned to the individual function blocks must be known to the shut down control device. Only thus can it assign the transmitted information about the internal states to its function blocks. In this process, incorrect assignment of the information about the internal states to the function blocks can easily occur.